A train is traveling with a speed of 15 m/s relative to earth. A passenger standing at the rear of the train pitches a baseball with a speed of 15 m/s relative to the train off the back end, in the direction opposite the motion of the train. (a) what is the velocity of the baseball relative to earth? (b) what is the velocity of the baseball relative to the earth if thrown in the opposite direction at the same speed?